Thirty-five people were detained by officers at a police training center under development outside Atlanta after they clashed with law enforcement Sunday, local police said.
It wasn't clear if the 35 were under arrest and, if so, what charges were being recommended.
The clashes erupted in the late afternoon and were punctuated by a few fires and the sound of firecrackers at the forested site of the Atlanta Public Safety Training Center in DeKalb County, south of Atlanta.
Police alleged in a Sunday night statement that a group of "outside agitators" showed up, changed into black clothing, and mounted a "coordinated attack on construction equipment and police officers."
"They began to throw large rocks, bricks, Molotov cocktails, and fireworks at police officers," the Atlanta Police Department said.
Part of the attack focused on the area under construction, the department said.
Organizers and supporters said the clashes took place amid a weekend concert, the South River Music Festival, and that most attendees were allowed to leave via shuttle or their own vehicles.
Organizers did not immediately respond to a request for comment. The Atlanta Solidarity Fund, which helps bail out people arrested at demonstrations, tweeted, "Police seem to be lashing out at anyone present at the music festival."
Police said demonstrators could have caused "bodily harm."
"Officers exercised restraint and used non-lethal enforcement to conduct arrests," police said.
On Jan. 18, police fatally shot a demonstrator later identified as Manuel Esteban Paez Teran but known as Tortuguita. Authorities said he opened fire on a state trooper who was injured but was expected to recover.
Even as the shooting remained under investigation it brought renewed attention to omnipresent demonstrations against the facility that have been organized under the slogan "Stop Cop City."
Protesters say they're both concerned about the center's environmental impact and its symbolism as one of the nation's largest law enforcement training centers at a time when police killings remain a heated topic.